Signal modulator is an important part of the digital modulation system. Key features of signal modulators are RF bandwidth, modulation bandwidth, local oscillation drive power and modulation accuracy. Several types of signal modulators are Gilbert mixers, diode mixers, reflective modulators and so on. The Gilbert mixers have the advantages of low loss, high harmonic suppression and high isolation, but have the disadvantage of lower operating frequency, usually only below 10-GHz, and ease of DC power consumption. The diode mixers have the disadvantage of requiring a higher drive power of the local oscillator signal. The reflective modulators have less influence on the phase and amplitude error caused by the process variation, and can have a wider operating bandwidth and lower required local oscillator drive power. However, reflective modulators have the disadvantage of low isolation. Moreover, the reflective modulators use more passive circuits, and thus required circuit area of the reflective modulators is quite affected by the operating frequency.
Accordingly, it is imperative to provide signal modulators which can overcome the aforesaid drawbacks of the conventional signal modulator(s).